Gyratory compactors are used to compact asphalt mixture specimens, among other substances. The measured properties of the compacted specimens are used to assess and predict pavement performance. Compaction in a gyratory compactor is achieved by applying a vertical consolidation force while the mold gyrates at a nominally constant angle. This angle is referred to as the angle of gyration. All gyratory compactors have a means for setting the angle of gyration, but it is desirable to have an independent means of verifying the angle since the angle is so critical to the measured properties of the compacted asphalt mixtures. Further, the angle is quite small and a slight variation from the desired angle makes a substantial change in the properties of the compacted asphalt mixture. It is also desirable to be able to measure the angle while the asphalt mixture is being compacted in order to detect any problems with the compactor as soon as they occur.
All compactors use a common mold to contain the asphalt being compacted; ideally, an angle measurement device would fit within this mold, thereby being usable in any compactor.
Accordingly, it is an object of the present invention to provide an angle measuring device for gyratory compactors which can be used with any compactor.
It is a further object of the present invention to provide an angle measuring device for gyratory compactors which provides a very accurate measurement of the angle of compaction.
It is a further object of the present invention to provide an angle measuring device for gyratory compactors which is placed within the mold in which the asphalt is being compacted.
It is a further object of the present invention to provide an angle measuring device for gyratory compactors which is a compact self-contained unit.
Briefly, the present invention is a self-contained unit which is placed in the bottom or top of the mold along with the asphalt mixture. The unit has two probes, in vertical alignment, which project out from its side and contact the inside of the mold. The probes are on a common carrier that is spring-biased outward in order to cancel out small amounts of off-center alignment of the unit within the mold. One probe is fixed relative to the carrier, the other can move independently of the carrier. The device is placed in the bottom of the mold of a gyratory compactor and the asphalt to be compacted is placed on top of it. As the mold oscillates, the independently-movable probe extends more than and less than the stationary probe; the difference in extensions is related to the angle of the mold and hence the angle of compaction.